Nyköping Municipality is a municipality in Södermanland County in southeast Sweden. Its seat is located in the city of Nyköping, which is containing a majority of the residents. Its southern tip in the district of Tunaberg is the southernmost point of mainland Svealand, one of the three original crowns forming Sweden. Nyköping is the administrative capital of Södermanland and hosts both the governors' residence and the regional council.

Södermanland County is a county or län on the southeast coast of Sweden. In the local Sörmlandic dialects it is virtually universally shortened and pronounced as Sörmlands län, or simply Sörmland, which is the dominant pronunciation and spelling inside the county. For example, the name of the local regional council is Region Sörmland. It borders the counties of Östergötland, Örebro, Västmanland, Uppsala, Stockholm and to the Baltic Sea. It holds the popular camping route called "Sörmlandsleden" which is a system of trails covering a total of approximately 100 mil (1000 km) of walking paths, in Södermanland. Prince Alexander, the son of Prince Carl Philip, is Duke of Södermanland.